The present application is related generally to systems and methods for communicating with nodes in a linear network and in particular to a system and method for communicating among and controlling rail vehicles.
For many years, railway freight trains have operated with pneumatic brakes for both the locomotive and the rail cars. In a typical system, the locomotive supplies pressurized air to the railcars through a brake pipe which extends the length of the train. The brake pipe of each rail car is typically connected to the brake pipe of adjacent vehicles via a flexible hose connector often called a glad hand. The brake pipe serves to supply both the pressurized air used by the railcars to drive their brake cylinders but also as a means for communicating when the railcars should apply or release their brakes. In a typical prior art pneumatic brake system, the locomotive commands the railcars to apply their air brakes by causing a drop in pressure (of 7 to 25 pounds of air) in the brake pipe. Each railway car, in turn, senses the drop in air pressure in the brake pipe and applies air from a local reservoir to the brake cylinder(s) on its wheels in an amount proportional to the changes in the brake pipe pressure and effects a stoppage of the train. When the brakes are to be released, the locomotive increases the pressure in the brake pipe, which is interpreted as a command to release the brakes by the rail cars.
The foregoing described pneumatic braking system has been used for many years and has the advantage of being entirely pneumatic. Such systems, however, are known to have several deficiencies. For example, because the command signal (the drop in air pressure) is a pneumatic signal, it must be propagated along the brake pipe. Accordingly, on long trains, it can take many seconds for the braking signal to propagate to the end of the train. Thus, for this period of propagation, not all the cars in the train are braking. Generally, the propagation of the braking signal is much less than the speed of sound for normal braking and the signal may need over a minute to propagate along a train of 150 cars. Because the braking applied is a function of the pressure change seen at each railcar, the precision to which the brake application can be controlled is degraded both by the propagation characteristics of the brake pipe and the leakage that is typically observed in the brake pipe closed pneumatic system.
In a typical prior art pneumatic braking system, there is no provision for partially releasing brakes. Once a brake release signal is received via the brake pipe, each rail car fully release its brakes. In many instances, it would be desirable for the train operator to be able to effect only a partial release, such as when too much braking has been applied in a train and it is desried to reduce the level of braking without fully releasing the brakes.
It is a further known limitation of many prior art railway braking systems that such systems do not provide for variability among the railcars in the amount of braking applied. When all railcars are braked in the same amount, some of the railcars will decelerate faster than others (e.g., empty cars will decelerate more quickly). Because the railcars are interconnected, the different braking results stemming from railcar characteristics can cause considerable forces to be generated between cars causing considerable stress on the car draft gear and coupler. Because of the in-train forces which can be generated by the variable effects of a single braking command, train operators must brake their trains judiciously, and generally, at less of a deceleration rate than would otherwise be possible to avoid uncouplings and derailings.
In the typical prior art pneumatic braking systems, it is also known that little additional information can be communicated along the brake pipe except for the relatively simple brake apply and release signals. For example, if a railcar in the middle of a train has a cargo that must be kept at a particular condition, there is no way in the typical pneumatic air brake system for monitoring the status of such a railcar and to provide a warning if the required conditions are not being experienced. For another example, it is highly desireable to learn immediately if a remote node has experienced a critical failure or emergency condition.
Over the last couple of decades, and particularly recently, electronic improvements to railway braking and control systems have been introduced. For example, communications have been established between plural locomotives, remote from each other, in a train so that a single operator can control the throttle and brakes of locomotives spaced throughout a train. This system, known as the LOCOTROL™ system, utilizes a radio frequency link between a lead locomotive and one or more trailing locomotives to control the throttle and braking at the various locomotives. The LOCOTROL system provides both for a more even pulling of the railcars and for an improved braking performance because each locomotive can effect the braking signals using the speed of the RF communications rather than the slower speed of the pneumatic brake pipe signal. For another example of the improvements already obtained by the use of electronics in the railway locomotives, in one electronic system, the pneumatic braking valves at the locomotive which control the brake pipe have been replaced by electronic sensors and actuators which provide for more reliable control of the brake pipe signals. In another change, braking systems have been proposed in which the brakes at each railcar are electronically operated in response to electrical signals carried by an electrical wire which passes through and between each railcar in a train. While a wired braking system provides the benefit of braking signal propagation at the speed of light, the wires which carry the braking signals from car to car are subjected to a harsh environment and may be susceptible to damage. Worse, a break or disconnection in the wire controlling the train will result in an undesired emergency braking of the train.
There is a considerable body of prior art related to the passing of messages among plural RF transceivers, which can be considered nodes in a radio network. It is known and often desirable to communicate among multiple nodes, each node having a transceiver capable of transmitting and receiving messages from other similar nodes. Often, such nodes are configured circularly about a master node and each of the nodes is well within range of each other and the master node. Under such circumstances, asynchronous protocols such as collision detection are adequate, as are synchronous protocols which rely on timing messages from a master node. However, if the nodes are not generally circular, such protocols may be unsuitable. For example, in a railroad train with two or more cars acting as nodes in a communications system, the network is generally linear and the last node in the network may vary substantially from the second node in its ability to communicate with the first node. While high-powered, robust transceivers could be used so that sufficient power is available to communicate with even the most remote nodes, such equipment is both relatively expensive and impractical for a railroad in which the cars are typically unpowered, requiring an associated transceiver to be based on battery or locally-generated power. Moreover, even if sufficient power is provided to the transceivers to communicate between the furthest nodes, trains frequently operate in a manner where portions of the train are out of communication for a variety of reasons. For example, tunnels can render a number of nodes in the train incommunicado for the length of the tunnel. Urban environments may have man-made obstructions blocking the line of sight between the beginning and end of the train. Natural objects likes mountains may also be interposed in the line of sight between the beginning and end of the train. Thus, even with increased transmission power, it is not possible to ensure continuous RF communications between all of the cars in a railroad train or other similar linear network.
Often the communications needs for linear topology networks require a high degree of reliability. Messages may need to be received by all the desired nodes to effect a change. For example, if a communications system is used to transmit braking commands from a locomotive to other locomotives or to cars within a train, it is critical that the commands be rapidly and reliably communicated to the desired nodes. Receipt of messages may be confirmed by the transmission of an acknowledgment signal back to the sending node. However, in a linear topology where the receiving node may have a different transmission power that the sending node and where the environment constantly changes, the receiving node may not be able to merely transmit an acknowledgment message which will be received at the original sending node. In such prior art systems, the failure of the original node to receive an acknowledgment usually entails another attempt at sending the original message to the same node. Clearly, if the intended receiver in fact received the original message, re-sending the unacknowledged message wastes the available massaging bandwidth of the system.
One way known in prior art systems to transmit messages along a linear network is to have each node in linear succession along the network receive, acknowledge and retransmit each message to the next successive node. With many nodes in the linear network, a train, for example, can have well over two hundred cars, the message may take an unacceptably long time to travel the length of the network, particularly if the RF environment is impaired. In addition, such systems are susceptible to blocking along the line of nodes if one or more nodes in succession are inoperative.
When the linear network is moving, as in the case of a railroad train, there are different problems than those encountered in a fixed location. For example, a train with a communications system will often encounter other trains as it moves down the tracks. If the two trains are using the same type of communications system, there must be a way to prevent the communications of the first train from interfering with or being mistaken for the communications of the second train.
Another serious problem faced by mobile linear networks is the fact that the surrounding environment is constantly changing. In such circumstances, nodes which are in communication at one point in time may be out of communication at still another point in time. The dynamic nature of node communication makes it difficult to reliably communicate within the nodes of a train as their geographic position and environment are constantly changing. One solution to this problem is to use a network with adjacent nodes communicating among one another. However, this solution is relatively slow and susceptible to blockage by the failure of one or more nodes. The long time required to complete a message may prohibit this solution. Further, this technique does not take into account the ability of a linear network to simultaneously transmit from multiple nodes when there are short range transmitters. In other words, the length of a linear network like a train may permit the network to operate in a time-bandwidth-space mode. The available bandwidth at one time may be used differently at different nodes in the linear network. As noted below, the present invention makes available time-bandwidth-space signaling which is particularly useful in linear networks such as long trains.
Accordingly, it is an object of the present invention to provide a novel communications system and method which obviates these and other problems of communicating among plural nodes.
It is another object of the present invention to provide a novel communications system and method which communicates efficiently along the nodes of a linear network.
It is yet another object of the present invention to provide a novel communications system and method of communicating along a network without the use of an external or master timing source.
It is still another object of the present invention to provide a novel communications system and method of communicating in a network in which the ability of particular nodes to communicate with other nodes varies over time.
It is a further object of the present invention to provide a novel communications system and method of communicating in a linear network in which messages are not blocked by the failure of one or more successive nodes.
It is yet a further object of the present invention to provide a novel communications system and method of communicating in a linear network in which messages are forwarded to a node that is several nodes away, that distance being reduced when required in order to provide reliable communications in adverse conditions.
It is still a further object of the present invention to provide a novel communications system and method for communicating among plural nodes which efficiently uses the available bandwidth, time and space to schedule the transmissions of messages.
It is another object of the present invention to provide a novel communications system and method of communicating in a linear network along a mobile network which avoids radio interference with other similar networks which are geographically proximate.
It is still another object of the present invention to provide a novel system and method of communicating in a railroad train environment which utilizes both diversity and redundancy to efficiently and reliably communicate messages.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of the preferred embodiments.